Hello guys,

I am getting a 12530283 L31 crate engine, and want to ensure that the following part numbers are what i need to go over .480 lift on the vortec heads, part numbers are from Summit.

COMP Cams 26915-16 - COMP Cams Valve Springs

COMP Cams 648-16 - COMP Cams Race Valve Lock

COMP Cams 787-16 - COMP Cams Steel Valve Spring Retainers

Also with an Edelbrock RPM air gap intake and Holley 65-3310 750 vac secondaries, and the follwing cam:

GM Performance 14097395 - GM Performance Hydraulic Roller Camshafts

Cam Style Hydraulic roller tappet
Intake Duration at 050 inch Lift 196
Exhaust Duration at 050 inch Lift 206
Duration at 050 inch Lift 196 int./206 exh.
Advertised Intake Duration 288
Advertised Exhaust Duration 308
Advertised Duration 288 int./308 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.431 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.451 in.
Valve Lift with Factory Rocker Arm Ratio 0.431 int./0.451 exh.
Lobe Separation (degrees) 109

what would the power estimate be in your opinion? or would you guys recommend a different cam since I am making the spring/retainer change?

Will i need new pushrods as well?

Has anyone used the following intake?
Professional Products 52028 - CrossWind Vortec Intake Manifolds

Any info would be greatly appreciated, let me know if you have any questions.

Kind regards,
naphtali

 

With the beehive springs, you should be able to get a little more lift. One thing to keep in mind is that, IIRC, the vortecs have SS exhaust valves with spun-welded stem faces that move the groove on the valvestem down. The spring seat is also lower, but the exhaust valve guide is at the same height as the intake. Consequently, the max lift at the exhaust will be the governing factor with stock valves as the seal is closer to the retainer on the exhaust valves. Measure the clearance between the valve guide seals and retainers once you have the springs. After that, then you can move to cam selection.

The cam you have there is REALLY tiny for the rest of the setup. That looks like its the specs of a stock L31 cam, which I assume is the one you have currently. Comp cams has extreme 4x4 cams, which are essentially low lift versions of their regular XE cams. You might want to look at those for use with your vortecs.

If your taking the heads off, then it might be worthwhile to just have them machined to square everything up and reduce the valveguides for more lift.

 

Thanks for the tip about those 4x4 cams... Looks like a good workaround to a custom grind.

Did a little searching, and I found this "Truck" cam:

http://www.summitracing.com/parts/CCA-12-413-8/
220/224 @ .50 and .474/.474 lift.

How do you guys think that would work with some Vortecs?

My current cam is 218/224 @ .50 and .462/.467 or so lift... you think that truck cam would be a big enough improvement over my flat tappet to be worth the trouble? I know the roller cams can open those valves amazingly quick, but is it enough to see a power difference with nearly the same specs on paper?

Says it's a retrofit roller camshaft though. How would that work with a 1pc RMS block that would need retro rollers? IE... a truck block like I have? Also, sorry to further derail the thread from the original poster, but I'm pretty sure my exhaust valves are +.100 inches, does that mean I get .1 more guide/retainer clearance? Seems like that kind of workaround is a little TOO easy... do most people not do that because valves are more expensive than special springs, or is there some reason that doesnt work?

 

AFAIK, the truck block is laid out pretty much the same as the older blocks as far as the timing set area is concerned. If the block has the bosses for the lifter spider and the deep lifter bores, then you can use stock roller lifters and a spider instead. The retro-roller lifters are essentially the same, but have link-bars instead to keep the lifters oriented with the cam. If you use aftermarket link-bar hydrolic lifters, go with ones made by Morel. Theyre available under various names like Isky and Lunati, but they seem to be one of the few that are reliable. Theyre expensive, but worth it in the end given the problems with comps stuff in the past.

Its hard to say how much of a gain you would see. The roller cams do have much steeper ramps as you dont have to worry about the lifter like you do with the flat tappet. I have the XE-258 4x4 cam, and with that along with my trickflow heads and victor intake, the power doesnt really start to come in until the engine gets to around 4000 RPM. It has almost the same power band as my old Isky 270 single pattern. The swap is expensive, but I would say that it would at least give some power gains due to the elimination of all the friction that you have with a flat tappet cam. I would say in reality you would probably see a noticable increase in power with a roller.

Its been a while since Ive messed with the vortec heads, but I would say the valves should give more clearance, but may require shimming or different springs to make it work. Moving the retainer away from the valve guide also moves it away from the spring seat. To see what would work would probably require some measuring. I remember the beehives and offset retainers giving at least .480" of lift with the stock valves. The max lift limit with the stock retainers on my old vortecs was exactly .460" before the retainer and seals met. My cam had .459" of lift, and was essentially smacking the retainers into the seals. I could even see marks on the VG seals from the retainers bumping into them. The max lift seems to vary from head to head, so its one of those cut and try deals.

If the heads are off the motor, then its probably easier to just machine them for bigger springs and such, especially if you want to go to a roller. Im using the 26915s with my cam (which also fit the vortecs) and it makes it to 6k without issue, but my cam has less lift than the one above.

 

thanks for the input dimented24x7, i really appreciate it. I was going to just change the spring/retainers/locks while the heads are still on the car, if i could find the right camshaft to make the most power with the stock heads without port/polishing work.
as stated in the OP i want to use the RPM air gap intake, or the Crosswind with the 3310 Holley.

This is where i got the idea about the spring/retainers:

http://www.hotrod.com/techarticles/e.../photo_10.html

Should i take your hint about taking the heads off and have them machined? Or is it possible to get enough cam to take advantage of the stock heads and intake/carb? with just the spring change?...when i measure from retainer to top of valve guide/seal how much under that number should i leave for clearance for the lift of the cam?

kind regards,
naphtali

 

http://www.alexsparts.com/products/V...YD-ROLLER.html

https://www.thirdgen.org/forums/tech...ortec-lt4.html

 

You can look into a small diameter double spring for hydraulic rollers and try running +.050" offset locks and then adding .050" of shims under neath the spring. This would raise the assembly .050" above the guide, giving you that much more clearance. This would essentially give you an increase from .460" lift stock to .510" or so.

That will cover anything you need with vortecs but like said above, you need to really measure each valve to see exactly what lift range you will have and leave abit of clearance between the retainer and guide for safety.

For vortecs I've seen alittle larger duration split since the exhaust side isnt that great, but the tight lobe seps seem to do well. I like the 4x4 grinds. The roller 220/224 would be a significant improvement over the flat tappet design. Rollers are smoother and will make more power due to improved lobe designs and lack of friction. Plus there is no cam break in and you can use whatever oil you choose, which is important since most oils today do not have enough zinc and other lubricants needed for flat tappets

 

thanks for the replies guys, i appreciate it.

based on research here and other forums I am going with the springs/retainers/locks i posted initially, that should take care of the retainer/seal bind issue, i really appreciate all the helpful info you have offered on the valve train questions.

Still undecided on cam, but like that LT4 cam, i really don't want the engine to have to spin high rpm's to make real good power/torque... say 5000 rpm, is that an ok rpm to try and stay under for a 4 bolt L31 with the RPM air gap and 750cfm 3310 holley ? would there be a better carb other than the holley?

also what headers would be best for this combo?

what stall speed converter do you recomend for my TH400?

Kind regards,
naphtali

 

You can take it to 6000 rpm if you use the LT4 hotcam.

My buddy's motor was a vortec 350 with vortec heads/RPM air gap intake, 750 double pumper carb with stock LT1 fbody cam. Dont know which LT1 cam but that setup he took to 5800 rpm like a stock Fbody and it ran mid 13's in a 83 shortbed pickup truck which is alot heavier than a fbody. Lt4 hotcam would pick up a good bit more power and still can shift by 6000.

The regular LT4 cam wouldnt be a bad choice either, its similar to the Lt1 cams, but i'd try to find them used instead of buying new from GM.

ZZ4 cam is also popular but its .520 lift on the exhaust, so you may need some extra work to get those in there.

 

Orr89RocZ,
That is really encouraging because to be honest with you guys, i have a 1986 Chevy Silverado SWB that I am dropping this motor in to replace a busted stock 305.

I came here to this forum because it apears the wealth of knowledge here outweighs most of the squarebody/C10 pickup sites, so feel good about that

Anyone else have an opinion on the LT4 hotcam, as I think I may go with it.

Also, will I need a new timing set for the LT4 hotcam, or will the stock one work... This will be a new crate engine, so the gears/chain will be new.

Kind regards,
naphtali

 

is the timing set new on the L31 motor? If not, get a new one. They stretch over time.

Reason I like the hotcam is that its a cheap cam when found used, and since LT1 guys use it ALOT you can find them for well under 150 bucks, which is good for a roller cam. It also makes good power, typical LT1's make 330whp with supporting bolt ons with that cam. Its capable of alot more with good heads. Possibly 350whp with vortecs since they flow abit more than LT1 heads. Just depends on the setup and tune.

 

I think my math says the intake duration on the hotcam is something like 204/213 and .492/.492 with 1.5 rockers. The duration is pretty hard to really determine, though. I just divided by 1.6 and multiplied by 1.5 - but I dont think it would really work that way with duration would it? Anyone know what the LT4 Hotcam's specs are with 1.5 rockers? Ive got a really nice set of 1.5 full roller Pro Mag rockers, I'd hate to have to swap them out for some stamped garbage to be able to afford a cam swap and get any decent power out of it.

 

It has the bosses and deep bores - but it doesnt have any of the machining necessary to be able to install the spider and dogbones.

 

Infernal,

Are you saying the L31 4 bolt main crate engine does not have the machining necessary? because it is a roller block, doesn't that mean it has all that already?

this is the crate engine i'm getting

http://www.sdparts.com/details/gm-go...gines/12530283

Kind regards,
naphtali

 

Any Vortec block will. That problem isnt anything you'll have to worry about. I have a 90-95 or so truck block. They still got flat tappet cams in the truck L05 engines, so they didnt bother finishing the roller cam hardware provisions. The block was cast to be a roller block, but never machined for it. In 1996 with the Vortec heads, they got roller cams. I was just asking for my own situation.

 

excellent.

do i need to worry about the cam dowel pin length on the LT4 hotcam when going into the L31 motor? or are they the same because they are both from roller blocks?

kind regards,
naphtali

 

it doesnt work that way, but the duration change would only be 1-3 deg difference if that. You'd have to plot the valve lift curve but from other simulations i've seen posted, it doesnt change much.


LT1 cam dowel is longer so it can drive the optispark I believe. Lt4 hotcam would come with the long pin. For a gen I sbc, all you need to do is cut the dowel pin down alittle. take a dremel tool cutoff wheel to it. I did my cam like that just fine

 

I can just bolt the timing gear on and then grind off the pin right?

kind regards,
naphtali

 

Yeah put the gear on, and see how far the pin sticks out, and then cut it off, almost flush with the gear.

 

ok guys i appreciate all the insight, i think that's it for now...

i'm going with the springs/retainers/locks from comp cams, and the LT4 hotcam suggested many many times on this forum. thanks for all the tips and tricks!

i'll be glad to get my engine so i can get it together

kind regards,
naphtali

 

My '95 truck block is fully machined even though it only came with a FT cam

'90 -00 L31 ( ( the one most commonly referred to as a Vortec engine even though GM called all their recent truck engines Vortec ) is a different casting # to the 87 - 95 truck blocks

 

Mine did not. I never went through the trouble to determine what year it was though, I just knew it was an L05 block.



Did I say something wrong?

 

A drill and a tap should solve that.

 

The factory mechanical red-line for the L31 was 5500 RPM. From my experience, the PM rods and cast pistons will work OK up to about 6k, but 5500 RPM is a good place to consider shifting, unless the car has an auto.

The power and torque/drivability are two different things. The power is a function of torque output and engine speed. Are you shooting for good power, good low end torque, or some mix of the two?

 

Hello demented,

I have a TH400, and i'd like to have a real good mix of the two for all around hotrod drivability , the parts i expect to use, will it be a good combo for that?
stock vortec 350 crate motor, rpm air gap, 750 holley, and LT4 hotcam?

kind regards,
naphtali

 

The LT4 hot cam will work well to deliver good mid range and top end power. One issue is that it will be on the high side of what you can do with a stock set of vortec heads. Youll probably want to decide how you want to do the heads first to get an idea of what the peak lift capability will be.

 

dimented,
thanks for your insight.
would a different cam be better since I am not going to change anything about the heads except the springs etc.? for me to get a decent all around balance of bottom, mid range, and top end...from idle up to the limit of the heads?

kind regards,
naphtali

 

that 4x4 cam I mentioned earlier could work.

It's similar to my flat tappet, and my car has a nice broad power band, sounds good at idle, and I have no complaints, I just want to trade some of that drivability for ridiculous power at this point. I've gotten too used to the power level.